Vibratory motor



y 1961 J. F. WAHL 2,986,662

VIBRATORY MOTOR Filed Nov. 6, 1958 FIG. 1

IN V EN T OR.

BY John F Wa/zZ 4 M 5 n mm Hiiornciqs Patented May 30, 1961 VIBRATORYMOTOR John F. Wahl, Sterling,

Ill. assignor to Wahl Cli er Corporation, Sterling, pp

This invention relates to a vibratory motor and more particularly to avibratory motor having an armature assembly which can be substantiallyundertuned without fluttering.

Present vibratory motors which operate on 60 cycle current (120 powerstrokes per second) have a natural tune frequency in the armature whichis higher than 80% of the driving frequency, i.e. 80% of 120 cycles persecond or higher than 96 cycles per second. Usually this tune frequencyexceeds 100 cycles per second. This condition is undesirable in certainrespects because vibratory motors will deliver more power and operatebetter generally when the armature assembly is undertuned to a greaterextent. However, when the armature assembly is substantially undertuned,i.e. tuned slightly below 96 cycles per second, there is a tendency forthe armature assembly to flutter, i.e. vibrate at a frequency of onehalf the driving frequency (60 cycle vibration in this case). Thisflutter is undesirable because the power output of the vibratory motorand the stroke length would be uncontrollable.

The reason that flutter occurs is that when the armature assembly isundertuned the predominant magnetic pull during normal operation occurswhen the armature is in an out position, i.e. at its greatest distancefrom the pole faces of the core. This magnetic pull must overcome theinertia of the armature moving away from the pole faces, stop, andreverse its motion so that it is moving toward the pole faces. Whenthere are no inertia forces on the armature moving away from the polefaces, as when the coil has been deenergized, the initial pull resultingfrom a high transient current upon energizing the coil will cause thearmature to strike the pole faces solidly. If this happens the next pullwill occur when the armature is out, and then again when the armature isin. The armature is thus operating at one half the desired frequency andwill have a long stroke and hammer against the pole faces withdestructive force.

It has been found that if the vibratory armature assembly is preventedfrom coming extremely close to the core of the motor or from contactingit, the above described condition leading to flutter can be avoided sothat the vibratory motor can operate effectively when the armatureassembly is tuned below 80% of the drive frequency.

What is needed therefore and comprises the principal object of thisinvention is an electromagnetic vibratory motor having substantiallyundertuned armature assembly which is provided with means for preventingarmature flutter.

A further object of this invention is to provide an electromagneticmotor with an undertuned armature assembly which is provided with meansfor preventing the armature from contacting the core of the motor.

These and other objects of this invention will become more apparent whenread in the light of the accompanying specification and drawing wherein:

Fig. 1 is a plan view of a hair cutter having an electric motorconstructed according to the principles of this invention;

Fig. 2 is an enlarged view of a portion of the armature assembly and thecore of the motor showing in dotted lines the motion of the armatureassembly toward the core of the motor, and

Fig. 3 is a sectional view taken on the line 3--3 of Fig. l and lookingin the direction indicated.

Referring now to Fig. 1 of the drawing, an electric clipper indicatedgenerally by the reference numeral 10 comprises a support or casing 12in which an electromagnetic vibratory motor 14 constructed according tothe principles of this invention is mounted. The vibratory motorcomprises a core 16 including an integrally attached centrally disposedelongated pole 18 with a pole face 20, see Fig. 2. Plastic molded andsomewhat resilient rims 22 and 24 are secured to pole 18 in spacedparallel relationship to each other to form a spool 26 and anelectromagnetic coil 28 is wound on this spool.

An armature assembly 30 including an armature 32 and parts (not shown)attached thereto for holding it on the clipper is secured to casing orsupport 12 for resilient vibratory movement. Armature 32 is disposedadjacent to pole face 20 in operative relationship therewith so that analternating current applied to coil 28 will cause the armature tovibrate. Free end 34 of the armature is connected to a movable cuttingblade 36 by any conventional means (not shown) so that the vibration ofthe armature will cause the movable cutting blade to oscillate relativeto a fixed cutting blade 37 in a manner well known in the art. Thearmature assembly is designed so its natural tune frequency is less thanthe driving frequency of the motor. In practical terms, this means thatthe armature assembly must have a natural frequency which is less than120 cycles per second because the usual household 60 cycle currentcauses an electromagnetic coil to supply two driving magnetic pulses percycle.

In the conventional electric hair clipper, if the armature assembly wassubstantially undertuned, i.e. tuned to around 91 cycles per second, theinitial magnetic pull caused by the high transient current of the coil28 and 'core 16 would occur when armature assembly 30 is at rest in aneutral position. This magnetic pull combined with the lower naturalvibratory frequency of the armature assembly causes the armature to bepulled solidly against the pole face 20. Since there is no air gap, thepulling force is extremely high. As the magnetic pulse decreases due tothe alternation in the current in coil 28 the armature assembly willmove away from the pole faces and will continue moving away from themfor an abnormally long stroke until the next magnetic pulse begins tooccur. The armature assembly of the conventional electric hair clippertuned below will continue to have two magnetic pulses per cycle and willthus flutter. As stated above, flutter is objectionable because of theunpredictable power output, stroke, and the generally destructive natureof its operation.

To prevent the armature from fluttering, stroke limiting means may bedisposed at or on any portion of the armature assembly or on the movablecutting blade. Such stroke limiting means may include placing anynon-magnetic resilient material between the pole face and the armatureassembly, or between any moving portion of the armature assembly 3% andthe core 16 for limiting the magnitude of the stroke of the armatureassembly as it moves in the direction of the core. It is noted, however,that the armature assembly will impinge against the stroke limitingmeans only on the initial strokes so as to prevent the armature frombeginning its flutter stroke, and will have no affect on the strokeduring continual normal operation.

In the illustrated device, the required stroke limiting means has beenprovided by giving the spool rim 22 an added function besides that ofretaining the electromagnetic coil on pole 18. To do this, somewhatresilient bosses 38 are integrally formed or molded on plastic rim 22and these bosses extend a small distance beyond the surface of pole face20 toward armature portion 32, see Fig. 3. The magnitude of thisdistance is sufiicient to keep armature portion 32 from reaching thepole face 20 or from approaching close enough to it to permit thearmature assembly to flutter and if portion 32 of the armature assemblyencounters these bosses, as seen in Pig. 2, their resilience preventsdamage to the armature and at the same time minimizes energy losses inthe armature due to the encounter. In actual practice a distance of .006to .008 inch has been found to work satisfactorily.

With this arrangement, the armature assembly can operate without flutterat a natural tune frequency which is as little as 75% of the drivingfrequency, i.e. 90 cycles per second When a 60 cycle current is suppliedto the electromagnet. In fact good results have been obtained when thenatural frequency of the armature is as low as 84 cycles/sec. The resultis that the motor 14 will deliver more power per wattage input to thecutter and it will operate more smoothly. Also, since the armature tuneis further from resonance, the detrimental effects of blade frictionhave less affect on the armature stroke length.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof as set forth in the claimsand the present embodiment is therefore to be considered as illustrativeand not restrictive and it is intended to include all changes which comewithin the scope and range of the claims.

I claim:

1. An electromagnetic vibratory unit comprising a support, a core havingat least one pole mounted on said support, said pole having at least onepole face, resilient rims on said pole forming a spool, a coil wound onsaid spool and adapted to be connected to a source of alternatingcurrent, an armature assembly including an armature and means holdingthe armature in position on said support, the natural frequency of saidarmature assembly less than twice the frequency of the alternatingcurrent to be connected to said coil, said armature positioned inoperative association with said pole face for vibratory movement, aportion of one rim extending beyond said pole face a distance less thanthe minimum distance of the armature from the pole face during steadyoperation so that the armature will contact said rim portion instead ofthe pole face only during an abnormally long initial stroke caused bytransient currents in the electromagnetic coil when same is firstenergized whereby armature flutter is prevented.

2. An electromagnetic vibratory unit for 60 cycle current comprising asupport, a core having at least one pole mounted on said support, saidpole having at least one pole face, a spool on said pole, said spoolhaving a rim with a surface adjacent said pole face, a coil on saidspool, an armature assembly including an armature and means holding thearmature in position on said support, said armature assembly having anatural frequency greater than 84 cycles per second but less than cyclesper second, the armature mounted for vibratory movement and positionedin operative association with said pole face, and resilient bossesintegrally formed with said rim on the surface thereof adjacent saidpole face, said bosses extending beyond the pole face and toward thearmature a distance less than the minimum distance of the armature fromthe pole face during steady operation so that the armature will contactsaid bosses instead of the pole face only during an abnormally longinitial stroke caused by transient currents in the electromagnetic coilwhen same is first energized, whereby armature flutter is prevented.

References Cited in the file of this patent UNITED STATES PATENTS1,684,260 Brown et al. Sept. 11, 1928 2,240,890 Kavle May 6, 1941FOREIGN PATENTS 925,885 Germany Mar. 31, 1955

